Effect of the O₂/Ar Pressure Ratio on the Microstructure and Surface Morphology of Epi-MgO/IBAD-MgO Templates for GdBa₂Cu₃O_7?δ Coated Conductors

High-quality epi-MgO buffer layers under different O₂/Ar pressure ratios are fabricated by rf magnetron sputtering on textured IBAD-MgO templates. Under the total deposition pressure remaining constant (14 Pa), the effect of changing the ratio of O₂/Ar pressure from 1:4 to 3:2 on the microstructure and surface morphology of epi-MgO films is studied. The microstructure and morphology of epi-MgO are fully characterized by x-ray diffraction, atom force microscope and scanning electron microscope. The best texture quality of epi-MgO with an out-plane Δω value of 1.8° and an in-plane Δ? value of 5.22° are obtained under the ratio of O₂/Ar pressure 3:2. Further, the surface morphology indicates that the surface of epi-MgO is smooth with rms surface roughness about 4.7 nm at O₂/Ar pressure ratio 3:2. After that, GdBa₂Cu₃O_7?δ (GBCO) layers are deposited on the CeO₂ cap layer buffered epi-MgO/IBAD-MgO templates to assess the efficiency of such a buffer layer stack. The critical current density of GBCO films (thickness of 200 nm) is higher than 3 MA/cm², indicating that epi-MgO/IBAD-MgO is promising for depositing superconducting layers with a higher critical current density.